Hacked Gadgets Forum

March 27, 2007

Alarm Phone Dialer – uses MT8880 and PIC 16F84A

at 2:17 pm. Filed under Cool Gadgets, DIY Hacks, Electronic Hacks

Just hook this Alarm Phone Dialer up to something you would like to monitor, for example, a high water alarm, low temperature alarm, back window, garage door, etc. When the system is activated it will call a number of programmed numbers to let you know the alarm has been activated. This would be great to get alerts of alarm conditions from your home when you are at work. The microcontroller code is provided on the site. The circuit uses a MT8880 DTMF dialer chip and a PIC 16F84A microcontroller. If you don’t feel up to the challenge of building your own dialer you can always look to the professionals to monitor anything you like with a modern security system.

“After putting together this little device, you must enter programming-mode to learn some phone numbers which this module will call after detecting an input on it’s sensor pin. After programming just supply power to the device. After pressing the button “Pokreni dojavu alarma” it will start to dial (tone or pulse, depending on the jumper setup). When the phone call is successfully established, the called party should press pound key “#” to stop the device from calling another number or again. You should put a sensor instead of button “Pokreni dojavu alarma”. Programming the numbers 1. press the “program” button 2. pick up the phone that is connected to the same phone-line as this device 3. punch-in first number and then “*” key 4. punch-in then next number and then “*” key 5. punch-in the rest of numbers, if more, and finalise with “*#” (example: 061123123*061456456*#) Please note: The device will learn 64 characters/digits including * and # keys.”
Thanks Muris.


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118 Responses to “Alarm Phone Dialer – uses MT8880 and PIC 16F84A”

  1. Alan Parekh Says:

    Hi David,

    To open the zip file that is located at the location linked to in the article please use any unzipping program such as Winzip

  2. BroHogan Says:

    Nice project! I just needed the phone line interface part and it works great. But I have a question about the .01uF 150V cap. I can’t figure out what it does! When the relay closes it is shorted out. With the relay open, you are on-hook and don’t need anything going to the isolation transformer.

    It seems it would only make sense if you need to monitor audio when on-hook. What am I missing?
    Thanks for any explanation.

  3. Sunil Says:


    The 0.01uF cap is a coupling capacitor. ( allows only the ac signals ) so that the phone draws no current when it is on-hook.
    But exchange circuitry can send an AC voltage down the line to activate the ringer for an incoming call.
    Its 150V cuz the telephone voltage during ring on ,on hook and off hook, the average voltage might reach above 100V (depends on various countries).

    **And by the way you dont need to monitor the audio when on-hook.
    Instead its on off-hook.During on-hook it waits for the ringer signal(AC signal) then sends a dc signal back to the exchange to stop the incoming ringer signal from the excange.

    The isolation transformer provides impedance matching so that proper communication takes place.
    i.e. The numbers dialed from another phone for feeding into the microcontroller’s eeprom should be properly processed by the microcontroller.
    Instead of an isolation transformer you can make use of any impedance matching devices.
    Even optocouplers do good.

  4. Muris Says:

    I left the 0.1uF capacitor in the circuit because I was experimenting with receiving DTMF between the first and the second ring, so it is for “future use” 🙂

  5. BroHogan Says:

    Muris, thanks for the reply – that explains it.
    I eventually went with a “DAA” as the phone interface. That turned out to be a much more solid interface for me. You can see details of the project at:

  6. Kyna Ng Says:

    hello, im going to do a project like this. can you sent me the program to learn some phone numbers which this module will call after detecting an input on it’s sensor pin.
    thanks alot.
    by the way, can it be wireless?

  7. tofi Says:

    plz can i have the c code for this project i really need it

  8. Garvish Raval Says:

    Hello Sunil & All,

    I am trying to build phone dialer with this reference circuit but not working for me here in India so can you please send me your eagle circuit to my email address, garvis.raval@volansystech.com or your and contact no ?

    What is ZD1V component ? Is it Zener diode of 1 Volt or some thing else ?

  9. Sunil Says:

    Heyya Garvish ,
    I tested this project on a bread board and it worked fine ..
    Wat kinda problems u got ??
    Power, Microcontroller not functioning or Not getting the call ..????

    and u r right … ZD1V means zener diode of 1V reverse breakdown ….

    U can post all doubts in this discussion in this site …

    sunil …

  10. ahmad itani Says:

    Do you have the flowchart of this project
    10x 😀

  11. Alan Parekh Says:

    Hi ahmad,

    There is a link in the article to more information.

  12. Ashique Says:

    Can anyone tell me where will I find this Isolated transformer?

  13. sunil Says:

    Hi Ashique,
    I could not find an isolated transformer in the market for loose.
    They sell it only in bulk. Its rare to find it loose.
    So I desoldered it off from an old dial-up modem. The new range of dial-up modems don’t have the transformer. Try searching an old one.


  14. kalusi Says:

    great job ,please can u add to is more details if i have take up this as a final year project i would need code for a particular micro controller

  15. Prokash Says:

    Any one tell me, what is the function of jammer?

  16. Luigi Fulk Says:

    Oh my goodness! a tremendous article dude. Thanks Nonetheless I am experiencing concern with ur rss . Don’t know why Unable to subscribe to it. Is there anybody getting identical rss problem? Anyone who knows kindly respond. Thnkx

  17. Bristol Security Says:

    A “real” burglar would cut the phone line (and prolly the power too) before entering the house!

  18. agung priyo Says:

    Hello my friends..
    I plan to install this alarm on my home, is there anyone could send me the source code, I would be very appreciate it. my e-mail id is apriyosATyahoo.com (please change AT to @) I’d be so so so very grateful if you could send it to me

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